So halfway through, I took apart the old optical block to see what kind of damage was inside. I pulled out the plastic carriage holding the polarizers, then the carriage holding the LCD panels. Here's what I found.
The green LCD panel, intact:
And here's the blue LCD panel, with the burned-in "halo" that not surprisingly matches the blue halo I had on my screen.
The green and red polarizers looked like this--pretty much untouched:
...but the blue polarizer did not fare so well. The polarizer actually appears to be a plastic film applied to glass, and you can easily see the amber discoloration, and the "burned in" area as well:
The real enemy of these sets is dust. There are four fans inside of my set, and I'm sure the others Sony made are similar. The optical block itself has two of them. There is a larger squirrel cage fan built into the bottom of the block that I did not yet get to, but here is the one that sits out in the open on top, forcing air past the bulb and lens, after I shot it with the compressed air briefly:
Beforehand, you can easily see how restricted the airflow was. There was a ton of dust in this thing. It's no wonder the sets failed. I'm not sure if this fan is 100% the cause, but I know from cleaning out my desktop computer (which was overheating also, the fans running in high speed mode constantly), it does not take much dust to restrict airflow.
So the bottom line is: in any of these rear projection sets, we may have to make it a habit to at least clean this one fan out regularly to prevent the LCDs and polarizers from getting cooked. I am hanging onto the two remaining LCD panels for future repairs, but I don't think the green and red polarizers can be used over the blue LCD. Otherwise, I can return the core to Tri State, and they'll reuse it for a future rebuild.
Total cost to me: $135, including the TV and the optical block. Not bad for a 50" HDTV!